Method of thermographic reproduction



June 1969 M00 YAMAISHITA ET AL 3,447,989

mmon OF THERMOGRAPHIC REPRODUCTION Fil ed Dec. 20, 1965 v lNVENTORs fiK/a yJ Wd'SJ/ 2 73m! Mi Su 2 uk/ MW 8, 1 M

ATTORNEYS United States Patent METHOD OF THERMOGRAPHIC REPRODUCTION Akio Yamashita and Takashi Suzuki, Ikeda-shi, Japan, as-

signors to Matsushita Electric Industrial Co., Ltd.,

Osaka, Japan, a corporation of Japan Filed Dec. 20, 1965, Ser. No. 515,082 Int. Cl. B44c 1/06; B41rn 5/26; B41c 1/06 US. Cl. 156-230 7 Claims ABSTRACT OF THE DISCLOSURE A method of thermographic reproduction comprising the steps of preparing a heat-sensitive sheet having solid fine particles of a stable supercoolable monomer uniformly dispersed on a support, exposing the sheet and an original to heat to produce a latent image formed from the solid fine particles of the supercoolable material kept at its supercooled state, transferring the latent image to the surface of a transfer material and effecting development of the transfer material.

This invention relates to a novel method of thermographic reproduction which utilizes the supercooling property of a stable supercoolable monomer.

Copying sheets used in conventional methods of thermographic reproduction have invariably contained all the materials required for the reproduction of images by heat exposure. Due to the above fact, the conventional methods of thermographic reproduction have involved such defects that non-sensitized copying sheets can difiicultly be preserved and, if a sensitized sheet were heated by some sort of mistake, reaction takes place at the non-sensitized portions of the sheet with the result that a good contrast between the already existing image portions and the remaining non-sensitized portions is lost. If, therefore, a method is discovered by which a developer can solely be applied to image portions on a copying sheet, the stability of the copy can remarkably be improved.

It is known in the art that a certain material has such a property that it would not solidify even when heated to melt and then allowed to cool down to a temperature below its melting point and remains in its liquid state. This property of such material is called the supercooling property, and it is also known that the supercooled state becomes more stable as the grain size of such material becomes smaller.

It is the primary object of the present invention to provide a novel method of thermographic reproduction in which advantage is taken of the supercooling property of a material of the kind described so as to form a latent image consisting of the material kept at the supercooled state, to transfer this latent image to the surface of other material and to visualize this transferred image for thereby obtaining a reproduced image having a good stability. More precisely, the present invention proposes a method of thermographic reproduction comprising the steps of preparing a heat-sensitive sheet having solid fine particles of a stable supercoolable material uniformly dispersed on a support, exposing said sheet and an original to heat to produce a latent image formed from the solid fine particles of the supercoolable material kept at its supercooled state, transferring said latent image to the surface of a transfer material, and effecting development on said transfer material.

The above and other objects, advantages and features of the present invention will become apparent from the following description with reference to the accompanying drawings, in which:

FIG. 1 is an explanatory view showing the successive steps of thermographic reproduction according to one form of the method of the invention; and

FIG. 2. is an explanatory view showing the successive steps of thermographic reproduction according to another form of the method of the invention.

The method according to the present invention is broadly divided into two forms. In the first form of the invention, image transfer is effected in simultaneous relation with heat exposure, while in the second form of the invention, image transfer is effected in suitably delayed relation with respect to heat exposure.

In FIG. 1 representing the first form of the invention, a transfer material 1 is brought into close contact with a heat-sensitive sheet comprising a heat-sensitive layer 3 formed from uniformly distributed fine particles of a supercoolable heat-sensitive monomer and a support 2 for the layer 3. The transfer material 1 and the heat-sensitive sheet are superposed on an original 5 carrying thereon an image 6, and infrared rays are irradiated onto the superposed sheet structure in a manner as shown by arrow 7 in FIG. 1a to melt those portions 4 of the heat-sensitive layer 3 on the heat-sensitive sheet which correspond to the image portions 6 on the original 5. The heat-sensitive material once heated to melt remains in its supercooled state and wets the corresponding surface portions of the transfer material 1. Then when the original 5 is removed from the heat-sensitive sheet and the heat-sensitive sheet is detached from the transfer material 1, the latent image 4 formed from the supercooled heat-sensitive material can be transferred to the transfer material 1, as shown in FIG. lb. Thereafter the transfer material 1 may be subjected to a developing treatment as will be described later to obtain a visible image 8 as shown in FIG. 10.

FIG. 2 represents the second form of the invention, that is, a case in which the heat exposure and image transfer are effected separately. In this form of thermographic reproduction, the heat-sensitive sheet is first superposed on the original 5 and infrared rays are irradiated onto the superposed sheet structure to form a supercooled latent image 4 on the heat-sensitive seet, as shown in FIG. 2a. The heat-sensitive sheet is then brought into contact with the transfer material 1 as shown in FIG. 2b and is subsequently detached therefrom to transfer the supercooled latent image 4 to the transfer material 1 as shown in FIG. 20. Thereafter, the transfer material 1 may be subjected to a developing treatment to obtain a visible image 8 as shown in FIG. 2d.

Although the case of the front printing in which the heat-sensitive sheet is placed closer towards the light source than the original has beenillustrated in FIGS. 1 and 2, the back printing in which the original is placed closer towards the light source than the heat-sensitive sheet may also be employed in lieu thereof. In the manner of thermographic reproduction shown in FIG. 1, the transfer material must be a material of sheet-like structure which can transmit the infrared rays, but it will be known that, in case the manner of thermographic reproduction as shown in FIG. 2 or the back printing is employed, the transfer material may be of opaque nature and is not limited to the sheet-like structure, provided that the surface to-which the image is transferred can make a close contact with the heat-sensitive sheet.

The developing treatment may broadly be divided into two forms. In the first form of the development, a developer such as a powder developer (toner) is externally applied to the transfer material, while in the second form, a developer is preliminarily included in the transfer material.

In the first form of the development, a powder developer is directly applied to the transferred latent image so as to be wetted by the supercooled heat-sensitive material in its liquid state and fixed thereto to give a visible image. If the transferred latent image has been urged from its supercooled liquid state to a solidified state due to a mechanical shock or the like caused during the transfer step, it is necessary to reheat the latent image to urge it again to its supercooled liquid state and then develop it. For this development, the dry developing process employed in the art of electrophotography is readily applicable.

An example of this type of development will be described below so that the invention can be understood on more materialized basis.

EXAMPLE 1 A heat-sensitive emulsion was prepared by heating 200 grams of triphenyl phosphate and a aqueous solution of gelatin at a temperature of about 70 C. and by emulsifying by an electrically driven agitator type emulsifier. This emulsion was coated on a cellulose triacetate film 50 thick and was allowed to dry to obtain a heatsensitive sheet. This heat-sensitive sheet was superposed on an original and, after heat exposure by a conventional heat exposure treatment, the heat-sensitive sheet Was detached from the original. Image transfer was then effected by superposing a polyester film 20 thick on that surface of the heat-sensitive sheet on which a latent image was formed. Then when the transferred image thus obtained was heated at a temperature of about 60 C. and the magnetic brush method was applied thereto, a visible image appeared on the polyester film.

An explanation will next be given with respect to the second form of the developing treatment in which a powder developer is preliminarily contained in the transfer material. Commonly, two kinds of materials reactionable with each other, that is, those materials which, when subjected to a simple treatment such as heating, can react with each other to develop a color are selected, and one of these two materials is held in the heat-sensitive sheet while the other is held in the transfer material. If these two materials include therein a material which has the supercooling property and has its melting point lying in a temperature range of 45 C. and 150 C. suitable for heat exposure, this material itself can be utilized as a heat-sensitive material. Aromatic amines are a typical material suitable for the heat-sensitive material. Experiments made by the inventors proved that almost all of the aromatic amines show-the superoooling property. Of these aromatic amines, those showing an especially stable superoooling property and suitable for the heat-sensitive material are diphenylamine, triphenylamine, p-toluidine, p-aminodiphenyl-amine, o-phenylene diamine, m-phenylenediamine, o-nitroaniline, m-nitroaniline, N-nitrosodiphenylamine, N-nitrosophenyl-benzylamine, and 2,4,6- tribromaniline. The aromatic amines easily react with various kinds of materials to make polymerization, condensation, cyclization or the like to form a colored compound. These reactions can effectively be applied to the method of reproduction according to the invention. Some examples of preferred combinations of these amines and materials which develop colors through reaction therewith are tabulated below.

Amine (heat-sensitive Color former (to be added (1 henyl me Reddish brown. 2, l-dichloro-a-naphtliol. Bluish purple.

o N-nitrosodiphenylamine Where any of the two kinds of materials developing a color through reaction with each other does not show the superoooling property, a suitable material may be added to one of these materials to improve the supercooling property, or one of these materials may be dispersed in the form of solid fine particles in a material showing a stable supercooling property for thereby obtaining a supercoolable heat-sensitive composition. As will be apparent from the foregoing, the heat-sensitive material is not limted to aromatic amines.

EXAMPLE 2 A composition consisting of 10 grams of N-nitrosodiphenylamine and 100 cc. of a 5% aqueous solution of polyvinyl alcohol was heated at a temperature of C. and was emulsified by an emulsifier. This emulsion was coated on a polyester film 20;]. thick and was dried at room temperature to obtain a heat-sensitive sheet. Then, a lusterless tracing paper was impregnated with a solution consisting of 3 grams of 2,4-dichloro-a-naphthol dissolved into cc. of toluene and was allowed to dry to obtain a transfer material. Heat exposure was then made in the manner as shown in FIG. 1 by use of these heatsensitive sheet and transfer material. Then when the transfer material Was detached from the heat-sensitive sheet and was heated at a temperature of about 100 C., an image of bluish purple could be obtained. This heatsensitive sheet could withstand more than five repeated uses.

According to the method of the present invention, it is possible to easily obtain a copy having images on both faces thereof. In obtaining images on both faces of a copy, a transfer material of sheet-like form having a slightly poor degree of visible ray transmission is employed and a latent image of a supercoolable heat-sensitive material is first formed on one face of the transfer material by the method of heat exposure as described previously. Before developing this latent image, the similar treatment is repeated to form another latent image on the other face of the transfer material. The latent images on both faces of the transfer material can be made visible by the developing treatment as described previously.

From the foregoing description, it will be apparent that, according to the method of the present invention, sufit ciently preservable copies can be obtained by dry developmg.

What we claim is:

1. A method of thermographic reproduction comprising the steps of preparing a heat-sensitive sheet having solid fine particles of stable supercoolable monomer uniformly dispersed on a support, exposing said sheet and an original to heat to produce a latent image formed from the solid fine particles of the supercoolable monomer kept at its supercooled state, transferring said latent image to the surface of a transfer material, and effecting development on said transfer material.

2. A method of thermographic reproduction according to claim 1, in which heat exposure is effected in a state that said transfer material is superposed on said heat-sensitive sheet and said heat-sensitive sheet is then detached from said transfer material.

3. A method of thermographic reproduction according to claim 1, in which the latent image is first formed on said heat-sensitive sheet, said heat-sensitive sheet is then brought into close contact with said transfer material, and said heat-sensitive sheet is subsequently detached from said transfer material.

4. A method of thermographic reproduction according to claim 1, in which a powder developer is used to develop the latent image obtained on said transfer material.

5. A method of thermographic reproduction according to claim 1, in which said transfer material contains therein a material which develops a color when mixed 5 6 and heated to melt with a solid material showing a stable References Cited supercooling property.

6. A method of thermographic reproduction according UNITED STATES PATENTS to claim 5, in which said solid material showing the sta- 2,260,612 7/1966 Dulmage et 117 '25 ble supercooling property is an aromatic amine.

7. A method of thermographic reproduction according 5 EARL BERGERT Pr'mary Examiner to claim 1, in which a first supercooled latent image is M. L. KATZ, Assistant Examiner. transferred to one face of said transfer material, a second supercooled latent image is transferred to the other face US. Cl. X.R.

of said transfer material prior to development of the first 117-36.1, 36.9 latent image, and then both of the first and second latent 10 images are developed. 

